1. Field of the Invention
The present invention relates to a carrier comprising carrier particles capable of imparting electric charges to toner particles when stirred together, and a two-component developer comprising the above-mentioned carrier component and toner component for use with the electrophotographic process.
2. Discussion of Background
According to the electrophotographic image formation process, a latent electrostatic image is formed on an image-bearing member such as a photoconductor, and the latent electrostatic image is then developed to a visible toner image by causing charged toner particles to deposit upon the electrostatic image. The toner image thus formed on the image-bearing member is transferred to an image-receiving material such as a sheet of paper, and fixed thereon by the application of heat, pressure, or solvent vapor thereto. Thus, output images are formed on the image-receiving sheet.
In the above-mentioned electrophotographic image formation process, the development system is roughly divided into two groups depending upon the method for charging the toner particles. One is a two-component development system employing a toner component and a carrier component, in which system toner particles are triboelectrically charged through the stirring operation with carrier particles; and the other is a one-component development system employing only the toner component. In the one-component development system, the toner particles are electrically charged without using the carrier. The one-component development is further divided into a magnetic one-component development method and a non-magnetic one-component development method, depending upon the factor whether a magnetic force is used or not for retaining the toner particles on the development roller.
In light of stable charging characteristics and rapid rise in the charging performance of toner particles, and stable image quality for an extended period of time, the two-component development method has become the mainstream in the copying machine that requires high-speed performance and excellent image reproducibility, and a complex system including such a kind of copying machine. On the other hand, the one-component development method is usually employed for a small-size printer and facsimile machine in view of the factors of space saving and low cost.
In recent years, recycle or reuse of the development unit mainly for the one-component development system has been realized in consideration of environmental destruction. At the same time, in the two-component development system, there is an increasing demand for extension of the life of the developer.
There has been a tendency to decrease the temperature for fixing a toner image from the viewpoint of reduction in consumption energy. Toner particles have been developed so that the toner particles can readily deform and be fixed at lower temperature.
The factors to cause the two-component developer to deteriorate are as follows: (1) wearing of the surface of carrier particles, (2) peeling of the surface coating layer of the carrier particles, (3) crashing of carrier particles, and (4) adhesion of toner component to the surface of carrier particles. Because of those factors, the charging imparting capability of carrier is impaired, a predetermined electric resistivity is varied, and minute fragments and cuttings are produced from the carrier particles. As a result, image quality of the obtained toner images is lowered, for example, a decrease in image density, occurrence of fogging on the background, and a decrease in resolution. In addition to the above, the image-bearing member is physically and/or electrically damaged, and a member for imparting electric charge to the toner is stained.
To solve the above-mentioned problems, there are many proposals. In particular, some proposals are made with special attention being paid to coated carrier particles prepared by providing a coating layer on the surface of magnetic particles.
Japanese Laid-Open Patent Application 9-269614 describes that the surface of carrier particles is coated with a resin coating layer which is prepared by dispersing resin particles and electroconductive finely-divided particles in a matrix resin in order to prevent the so-called spent toner phenomenon from happening for a long period of time.
Japanese Laid-Open Patent Application 9-311504 proposes carrier particles. Each particle comprises a spherical complex core particle comprising an iron oxide particles and hardened phenolic resin, and a surface layer comprising a hardened amino-group-containing phenolic resin, provided on the core particle, with the amount ratio of the iron oxide particles and the content of amino group in the amino-group-containing phenolic resin being particularly specified. This structure of carrier particles is considered effective for obtaining stable triboelectric charging characteristics and durability.
A carrier disclosed in Japanese Laid-Open Patent Application 9-311505 comprises carrier particles, each carrier particle comprising a spherical complex core particle comprising iron oxide particles and hardened phenolic resin. Those core particles are coated with a resin layer prepared by curing a mixture of phenolic resin and at least one resin selected from the group consisting of melamine resin, aniline resin, and urea resin. The carrier thus obtained is superior in terms of triboelectric charging characteristics and durability.
Carrier particles disclosed in Japanese Laid-Open Patent Application 10-198078 are constructed by providing a surface coating layer on core particles, the surface coating layer comprising a matrix resin, and finely-divided resin particles and finely-divided electroconductive particles which particles are dispersed in the matrix resin. Further, the matrix resin for use in the coating layer of the carrier particles contains the same resin component as that constitutes a binder resin for use in toner particles in an amount of 10 wt. % or more. Owing to such a structure, the charge imparting capability of the carrier is not hindered by the spent toner phenomenon.
Japanese Patent 2779976 discloses a magnetic carrier which is prepared by coating core particles comprising ferromagnetic particles and hardened phenolic resin with at least one resin selected from the group consisting of epoxy resin, polyester resin, styrene resin, silicone resin, and fluorine-containing resin. The magnetic carrier thus prepared is considered to have controlled charging quantity.
Japanese Patent 2825295 discloses a magnetic carrier which is prepared by coating core particles comprising ferromagnetic particles and hardened phenolic resin with a melamine resin. The magnetic carrier thus prepared exhibits high electric resistivity and small bulk density.
Japanese Patent 2905563 discloses a magnetic carrier which is prepared by uniformly coating core particles comprising ferromagnetic particles and hardened phenolic resin with a polyamide resin. The magnetic carrier thus prepared exhibits high electric resistivity and small bulk density.
However, the above-mentioned proposals cannot produce sufficient results contrary to expectations of low image fixing temperature and long-life carrier particles.
More specifically, in Japanese Laid-Open Patent Application 9-269614, most part of the surface of the carrier particle is occupied with the matrix resin. Therefore, it mainly depends upon the surface condition of the matrix resin whether the adhesion of toner component to the surface of the carrier particle can be prevented or not. Namely, the spent toner phenomenon cannot be always prevented from happening.
In Japanese Laid-Open Patent Application 10-198078, the same resin component as employed in the binder resin of toner composition is contained in the surface layer of the carrier particles. When the toner is designed to have a lower image-fixing temperature, the resin component common to the carrier particle and the toner particle tends to adhere to each other. The charge quantity of toner is apt to be low and unstable even at the beginning of stirring step.
The carrier in Japanese Laid-Open Patent Application 9-311505 is expected to meet both the requirements of charge imparting capability and durability to some extent by properly choosing the combination of resins for use in the surface coating layer of the carrier particles and optimizing the complex condition of the surface coating layer of the carrier particles. However, according to the proposal disclosed in the above-mentioned application, the resin composition coated on the surface of the carrier particles is homogeneous. There is no description about the microscopically observed surface condition of the carrier particles. Namely, the problem still remains that the surface condition of the carrier particles is impaired by friction between the toner particles and the carrier particles in practice. Although the composition of the surface layer of the carrier particles is specified in the application, the surface layer of the carrier particles cannot necessarily prevent the toner component from sticking to the surface of the carrier particles.
In the two-component developer, the toner particles and carrier particles are stirred together to cause triboelectric charging. However, as previously mentioned, the surface condition of the carrier particles required to impart sufficient electric charge to the toner particles, while preventing the toner component from adhering to the carrier particles has never been clarified. To satisfy both requirements, that is, to impart sufficient electric charge to toner and to extend the life of the carrier particles is still an object that has not yet been attained.
In light of the above-mentioned problems, it is a first object of the present invention to provide a carrier capable of preventing the toner component from adhering to the carrier particles and minimizing the wear of the surface layer of carrier particles. In other words, the first object is to provide a carrier having a long life, which can constantly impart sufficient electric charge to the toner particles for an extended period of time.
A second object of the present invention is to provide a two-component developer comprising the above-mentioned carrier.
A third object of the present invention is to provide a developer container.
A fourth object of the present invention is to provide an electrophotographic image forming apparatus.
The first object of the present invention can be achieved by a carrier comprising carrier particles, each carrier particle comprising a core particle comprising at least a magnetic material and a surface coating layer provided on the core particle comprising at least a resin, the surface coating layer being constituted of a plurality of regions, the regions being separately formed and joined together to form a surface complex configuration, and having different phase lags when the surface coating layer is subjected to scanning by phase imaging measurement using a scanning probe microscope in a tapping mode, wherein a region having a phase lag over the average phase lag obtained from Eavg=xcexa3(E(i)xc2x7S(i))/xcexa3S(i) has an area SO, and SO and xcexa3S(i) are in a relationship of 10%xe2x89xa6SO/xcexa3S(i)xc3x97100xe2x89xa690% when each region comprises a component A(i) having an area S(i) and a phase lag E(i), in which i represents the number of regions with different phase lags.
The second object of the present invention can be achieved by a two-component developer comprising a toner and the above-mentioned carrier, the toner comprising toner particles, each toner particle comprising a binder resin and a coloring agent.
The third object of the present invention can be achieved by a developer container which is filled with the above-mentioned two-component developer.
The fourth object of the present invention can be achieved by an electrophotographic image forming apparatus comprising the above-mentioned developer container.